text:
May turn rate indicators (and turn coordinators) be calibrated to be accurate at all airspeeds, or only for one?
2 related questions: may a turn rate indicator be calibrated to be accurate at all airspeeds, or only for one? Likewise for a turn "coordinator".
The meaning of "accurate" intended in this question is this: -- if the instrument is labelled "2 minute turn" and we fly for 2 minutes with the needle at the calibrated index, we accomplish 360 degrees of heading change, not more or less.
Some added context: note that if the bank angle is very steep, a turn involves mostly pitch rotation, not yaw rotation.  Consider the related question What is the formula for the bank angle required for a turn in line-abreast formation? -- several answers indicate that an aircraft flying at a higher airspeed and larger turn radius needs more bank angle to complete a turn in the same time than an aircraft flying at a lower airspeed and smaller turn radius.  Therefore the faster aircraft will be turning with more pitch rotation and less yaw rotation, and a given turn rate indicator could not read exactly the same in both aircraft, IF the instrument only measured yaw rotation.
So the essence of this question is-- can a turn rate indicator accurately measure the rotation component of a turn that involves pitch rotation rather than yaw rotation?  Is this true at all airspeeds, or only in a limited range?  Is any shortcoming in this regard significant in actual instrument flying?  Is the same true of a turn coordinator, or will it tend to be accurate  only in a narrower range of airspeeds than a turn rate indicator?

There is a highly related question out there already https://aviation.stackexchange.com/questions/27666/are-turn-and-slip-indicators-calibrated-to-a-certain-speed-if-so-what-speed , but it is not clear to me that it has any good answers.  Also, my question is asking specifically about both turn rate indicators and turn coordinators.  Basically, it seems that both instruments are usually calibrated on the assumption that the turn involves 100% yaw and zero % pitch, which does introduce some small speed-related inaccuracies.

What do you mean by "accurate"? To my knowledge, what a turn-and-slip indicator or a turn coordinator does is completely unrelated to airspeed, so if it reads accurately at one airspeed, it will read accurately at all airspeeds. For that matter, it'll read accurately under the sea or in outer space. But I think you have a different idea than me about how a turn coordinator is supposed to read.

@TannerSwett-- did that clarification help?

Yes, it did, thank you!

Really a duplicate of https://aviation.stackexchange.com/questions/27666/are-turn-and-slip-indicators-calibrated-to-a-certain-speed-if-so-what-speed

Turn rate indicators are calibrated to Rate 1, 2 and 3 turns at a
  specific TAS. A rate 1 turn is 180° a minute or 3° a second. A rate 2
  turn is twice that, 360° a minute or 6° a second.  A rate 3 turn is
  three times as much, 540° a minute or 9° a second. The angle of bank
  required to achieve a given rate of turn increases with the TAS.
It is inherent in the design of the instrument that in any yaw
  condition the gyro axis will tilt. and the gyro will become sensitive
  to pitch rate.
If the aircraft is then rapidly pitched nose up (in a loop or recovery
  from a spiral dive) this pitch input can deflect the gyro to read
  maximum turn rate. This is called looping error. This pitch rate error
  also affects the instrument readings in normal turns.
To compensate for this and for the difference between yaw and turn
  rates the indicators are calibrated to show rates of turn correctly in
  balanced turns for Rate 1, 2 and 3 turns at specific angles of bank
  and TAS.
Although the indicated rate of turn will be incorrect at speeds away
  from these datums the errors are not significant in normal operation.

Source

Turn coordinators are considered less useful than turn rate indicators because the gyro on a TC is at a 30 degree angle and turning in the reverse direction. This makes the instrument sensitive to G force, and it under reads as you pull G's in a turn. The only way I know of to counteract this is to push the yoke/stick forward to bring the G's back to 1. That said, different pilots have different opinions about all this so your mileage may vary depending on who you talk to.

"It is inherent in the design of the instrument that in any yaw condition the gyro axis will tilt. and the gyro will become sensitive to pitch rate." Is this saying that the gyro axis will tilt relative to the aircraft, and it will become sensitive to rotation about the aircraft's lateral axis? Or is it saying that the gyro axis will tilt along with the aircraft and it will be sensitive to changes in the aircraft's pitch (the amount by which the nose is pointing above or below the horizon)?

The theory is explained here: https://en.wikipedia.org/wiki/Turn_and_slip_indicator#Turn_indicator

@JuanJimenez -- this is really a better question -- https://aviation.stackexchange.com/questions/27666/are-turn-and-slip-indicators-calibrated-to-a-certain-speed-if-so-what-speed -- consider posting your answer there too -- I'm considering deleting the present question.

@JuanJimenez -- the url attached to your link "Source" is now behind a paywall.  This answer would benefit greatly from saying what the actual source is.  It goes to an airline pilot's forum, but did the quote on the forum cite a specific published source?  Thanks.

@quietflyer No, it is not. Requiring registration to view content is not a "paywall". The site doesn't charge anything.

@JuanJimenez -- I did register and I had to pay.  It appears to be a new thing.

Re the registration/ paywall thing-- I did google the text and found a different on line link, but still would be interested to know whether it was the same source cited in your link or whether different textbooks are using the exact same verbiage copied from an official government source or something as sometimes happens in flight training literature.  The link I found was https://issuu.com/bristolgs/docs/022a_inst_atpl_a__v6.1.5_ch_3_gyros/15 .

Never mind my comment about the direction of rotation of the gyro of the Turn Coordinator-- I think what you describe may be the norm but apparently it is not always that way-- I made a new question about it --
https://aviation.stackexchange.com/questions/81983/in-various-different-makes-and-models-of-turn-coordinators-do-the-gyro-wheels/81988#81988

A turn rate indicator measures only the angular rate of heading change. A turn coordinator measures both the angular rate of heading change and the angular rate of bank change. They are not effected by airspeed.
Your line abreast question should be asked separately. But the outside plane must travel faster and have more bank than the inside plane.

@MaxPower-- this is really a better question -- https://aviation.stackexchange.com/questions/27666/are-turn-and-slip-indicators-calibrated-to-a-certain-speed-if-so-what-speed -- consider posting your answer there too -- I'm considering deleting the present question.

Based on the related answer What is the formula for the bank angle required for a turn in line-abreast formation? , it appears that aircraft flying at different airspeeds will require different bank angles to carry out 360 degrees of heading change in a set time period.  At a steep bank angle, 360 degrees of heading change requires more pitch rotation, and less yaw rotation, than at a shallow bank angle.  If a "turn rate indicator" only detected the rate of yaw rotation, it could only be calibrated to read correctly at one particular airspeed.
A "turn coordinator" is similar to a "turn rate indicator", but the axis of rotation of the gyro is canted to sense roll as well as yaw.  However, in a constant-altitude turn, the roll rotation rate must be zero, and thus the situation is fundamentally no different than is the case with the "turn rate indicator".
The shallow bank angle involved in standard-rate turns in most aircraft minimizes these errors, in most aircraft.  An obvious exception would be an aircraft flying at very high airspeed, where a standard-rate turn would involve a rather high bank angle, and this would involve a higher percentage of pitch rotation and a lower percentage of yaw rotation than would be would be the case at a shallower bank angle, causing a turn rate indicator to tend to read abnormally low, if only yaw rotation were detected.
Some related outside reading -- https://www.pprune.org/tech-log/528255-turn-rate-indicator-turn-coordinator-looping-error.html , https://www.pprune.org/tech-log/82721-turn-gyro-axis.html , During "partial panel" flying, in what ways is a turn rate indicator more useful than a turn coordinator? .  The long and short of it seems to be that the design of these instruments is complex and somewhat varied.  In actual practice, any slight error in a stabilized turn due to the calibration being only valid for one airspeed is the least of a pilot's worries when flying blind.  Furthermore it appears that in most turn rate indicators, the gyro cants during a turn in such a way that it is closer to vertical and so does measure something closer to the actual turn rate, than just yaw rate alone.  It appears that this is never perfectly true at all airspeeds, and so the calibration of the instrument may only be perfectly accurate at one airspeed.  It appears that instruments designed with weaker centering springs will more accurately read the true turn rate in a stabilized turn, yet will also severely over-read when excess "G" is applied.  It appears that turn coordinators are generally accurate over a narrower range of airspeeds than turn rate indicators are, due to the differences in design-- it appears that there is little or no sensing of pitch rotation, or possibly even a wrong-way sensing of pitch rotation even in a stabilized turn, in the case of a turn coordinator.

Doesn’t the turn rate indicator scale stop at something like 30°? Maybe up to that bank angle, error is below x% with x being generally accepted, and above that the concept becomes less relevant anyway?

Far from a perfect answer yet, but a start

If you are concerned about the accuracy at differing airspeeds I would suggest you gather empirical data.  Next time you go flying drop the flaps and stabilize at some comfortable minimum airspeed and perform a standard rate turn, timing yourself to see how long it takes to perform a 360.  Then accelerate to a max airspeed and perform the same test.  I would wager that the accuracy of the instrument at different airspeeds exceeds your (and mine) ability to nail the turn.

A more refined version of this answer may now be found here -- https://aviation.stackexchange.com/a/81919/34686


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What law enforcement agency owns the airplane continually circling over south Wichita KS right now 8:45-9:15 AM CDT 3-11-24?
What law enforcement agency owns the airplane continually circling over south Wichita KS right now 8:45-9:15 AM CDT 3-11-24?
Details:  estimated altitude 2500-3000' AGL.  High-wing Cessna, 182 or larger, with struts, fixed tricycle landing gear.  LIDAR or TV or FLIR camera turret on underside, aft of cabin, left of aircraft centerline.  White, except upper 2/3 of vertical fin dark, upper part of fuselage from just aft of cabin to front of nose dark from a few inches below bottom of windows on upwards, wingtip fairings dark.  Dark color is black or dark blue.  Flaps are extended about 10 degrees.
I can't find them on FlightAware or FlightRadar24.
A plane was also doing similar circles for over an hour last night but likely a bit lower, almost certainly the same plane.
Bonus question: what are they doing?  Why so much circling over the city?

Still circling 9:30, south of Kellogg street (K-54/US-400), likely over or a bit east of I-135

Circling again now 3/15/25 21:10 CDT, guessing likely same a/c, bright white lights just inboard of wingtip navigation lights

Still circling 9:45 but a bit further north, think I just got the answer, last 2 digits of N# are "HP", maybe "N..........0HP".  Relevant: https://kansashighwaypatrol.gov/find-a-troop/troop-location-map/special-operations/troop-t-aircraft/ -- so likely a Cessna 206.  See https://registry.faa.gov/aircraftinquiry/Search/NameResult?nametxt=KANSAS+HIGHWAY+PATROL&sort_option=1.  Matches this paint scheme https://photos.flightaware.com/photos/retriever/99766af79f9b2dd02f16dcc273ad5081b58a086c from https://www.flightaware.com/live/flight/N940HP.
N900HP, N940HP, and N950HP all appear to be possible candidates (all Cessna 206's, and FlightAware shows similar paint schemes on all three), although the KHP website indicates that only two out these three have the FLIR camera, which is presumably the object visible aft of the cabin in the photo.  Image below is from link above.

this seems fairly accurate for finding it. if they aren't transmitting ADSB, sometimes you'll get lucky with TIS-B to see the circling (it'll show up on globe.adsbexchange.com). The other good place is liveatc; they are probably communicating with an "idaho" call sign, eg "Idaho 11". They're allowed to turn ADSB off when operational.

@300D7309EF17 -- re "They're allowed to turn ADSB off when operational. " -- thanks for mentioning that

Different paint scheme, but the Civil Air Patrol uses similarly equipped Cessnas, for Predator/Reaper UAV training. https://www.airandspaceforces.com/article/cap-joins-the-total-force/

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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Did the dog-tooth notches in the wing of the F-8 Crusader really have anything to do with "yaw stability"?
What was the real function of the "dog-tooth" notches in the leading edge of the wing of the Vought F8U crusader?
Wikipedia says:1

Vought's design team... produced... a relatively unorthodox fighter
that possessed... dog-tooth notching at the wing folds for improved
yaw stability

I find it hard to believe that any potential yaw stability deficit would not be addressed simply by increasing the (already ample) size of the vertical fin.
Did the "dog-tooth notches" really have anything to do with yaw stability?
Footnotes:

Link https://en.wikipedia.org/wiki/Vought_F-8_Crusader#Design, accessed 7/30/2023

It's my idea that a dog-tooth on the leading edge will decrease stall speed. You can also find them on the F/A-18 and MiG-23

Btw it appears that the wording of that sentence on Wikipedia has been substantially changed in the short time since this question was posted-- but the substance of the comments about the various design features remains essentially the same, including the claim that the dog-tooth notching improved yaw stability.

I don't know. I'm definitely not an expert yet. But I guess that's the reason why we're here

The usual way in which such devices work is that they provide a barrier between separated flow and the ailerons. The vortex coming from the notch ensures that the flow separation from the inboard wing cannot spread easily to the outboard wing and impair aileron effectiveness.
As such, it is useful for stability, but roll-stability, not yaw-stability.

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Do civilian aircraft transiting through controlled airspace designated for military airports typically talk to the tower of that airport? (USA)
The general point of this question is to understand how civilian aircraft operate around controlled airspace designated for military airports, in terms of communications, in the US.  I think the best way to phrase it is to give a few of specific examples--
The image below shows the airspace around Wichita KS.  My question is about civilian aircraft transiting through the Class D airspace designated for McConnell Air Force Base (KIAB).  The ground level in this area is around 1300' MSL, so an aircraft below about 1400' AGL would be below the overlying Class C shelf designated for Eisenhower National Airport (KICT).  I know civilian airplanes on pipeline patrol missions sometimes fly as low as about 500' AGL on a flight path that takes them roughly along the course of the river that flows through the SW portion of the KIAB Class D airspace, approaching within about 1.5 miles of the nearest runway of KIAB.
Would the pilot of such an aircraft, assuming that he/she is flying VFR and has no intention of actually landing (or shooting an approach) at KIAB, typically be talking to the tower at KIAB?  Or would the pilot more likely be talking only to civilian entities, such as the tower at KICT, or Wichita Approach Control?
If it matters -- which I'm not sure that it would-- assume that the flight originated at KICT, flew due east to the river, then followed the river though the KIAB Class D airspace at roughly 500' AGL/ 1400' MSL, exiting KIAB airspace in a generally southerly direction.
Similarly, what about a civilian aircraft doing pattern work at Beech Factory airport (KBEC) when the KBEC tower was open and the KBEC Class D was therefore in effect?  Would the pilot of such an aircraft typically be talking to the tower at KIAB whenever the aircraft was in the KIAB Class D airspace?  Or would communications more likely be handled entirely by the tower at KBEC, even when the aircraft was in the KIAB Class D airspace?
And what about a civilian aircraft doing pattern work at Beech Factory airport (KBEC) when the KBEC tower was closed and the KBEC Class D airspace therefore had reverted to surface-level Class E airspace?  Again, would the pilot of such an aircraft typically be talking to the tower at KIAB whenever the aircraft was in the KIAB Class D airspace?  Or would communications more likely be handled entirely by a civilian entity, such as Wichita Approach Control?

Military ATC facilities in the USA follow the same rules and procedures as civilian ATC facilities. There are a very few differences; certain branches of the military require Tower controllers to say "check wheels down" to all aircraft when issuing a landing clearance, for example, or require controllers to state the current wind with every takeoff clearance instead of only when a tailwind component exists. But for the most part everything is the same.
This means that yes, if a civilian pilot is within airspace controlled by a military ATC facility they are expected to communicate with that facility just the same as if the airspace was controlled by a civilian ATC facility.
You may not be permitted to land at a military airport, but that's an administrative decision which is made much higher up than the air traffic controllers talking on the radio.
As you can see from this map depicting TRACON airspace (more versions available at my answer here) it's not just Towers that are run by the military. If you're flying a long cross-country from the Wichita area to Illinois you could be instructed to "Contact Whiteman Approach" just as easily as "Contact Kansas City Approach." The only way you would know you were talking to a military approach facility would be the higher proportion of callsigns like "DOOM12" that you would overhear on the radio.

I've seen one case where banner tow aircraft operating east-west offshore about a mile (or less) from an Air Force base's runway 18/36 did talk to the military tower. Offhand I can think of two cases where airline traffic routinely talks to military approach controllers on their way in to non-military fields, and there are probably several more of those I'm not coming up with immediately.
Local airspace with multiple fields in close proximity can be complicated, and the different towers & approach control facilities can have letters of agreement how they will handle traffic doing particular things in particular places, so the best bet to find out about how things work in Wichita would be to call one of the facilities there and ask. You may have to wait while they transfer you to the right person (i.e. an actual controller or supervisor), but facilities like this are generally quite willing to discuss how they handle this sort of thing. That's especially true since a conversation before the flight can save everybody -- themselves included -- some tense moments if things go badly during the flight!

I can think of tower and approach examples in WA, CA, and AZ.

@tedder, see my answer. Military-run approach controls own airspace in more than half of the 50 states.

Frankly, you treat their airspace like you would any other class D airspace. The only thing required to enter is two way radio communications.  Their controllers may divert you to other areas of the air space to stay away from the immediate vicinity of the airbase, but other than that, operations would be identical to any other civilian towered airport with class D surface airspace surrounding it.
You can also contact Wichita approach.  Their TRACON remains in contact with the controllers out at McConnell and may elect to divert traffic through the Class D, if McConnell controllers are having a light traffic day.
Again, keep in mind that the national airspace system, in and of itself, is a joint civilian and military operated space in order to provide for flight operations within the United States.  There is no separate space for the military only.
I have a little bit of experience operating around Wichita. I have never flown out of the Beech as KBEC is a factory airport for Textron; there are no FBOs on the field and most of the local flight training is done out at Jabara (KAAO) or Augusta (3AU). I believe both Beech Tower and McConnell have letters of understanding concerning flight operations out there.
Oddly enough, most controllers at military airfields are very easy to deal with. Like I said, they may vector you away from the immediate vicinity of the airfield, or ask you to depart the airspace if they have a high volume of traffic coming in and out. For example, the controllers out at Nellis AFB in Las Vegas will probably ask you to remain clear of their airspace during Red Flag operations.  Workload permitting otherwise, there’s no problem with you flying in their airspace, and they will often let you shoot instrument approaches there, provided you go missed.  When I did my Instrument check-ride in 2011, one of the approaches I flew was the ILS Rwy 28 into Hunter AAF (KSVN) in Savannah, GA.  You would typically contact Savannah approach about doing that first, and the TRACON would contact Hunter controllers to see if their operations were light enough to accommodate.  Their controllers actually like to have fixed wing traffic going in there, because they were most likely going to begin careers as civilian air traffic controllers outside of the army and like getting the practice working with fixed wing aircraft.
In the example you cite, departing Eisenhower (KICT) you would be immediately handed over to Wichita approach, who may have instructions for you regarding operations in McConnell’s class D, as they at least technically control the Delta not in the immediate vicinity of the airbase and may hold letters of understanding between their tower and the TRACON.

Re "Wichita approach ... as they at least technically control the Delta not in the immediate vicinity of the airbase"  -- can you explain a bit more about how we know this to be true?


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Does does turning into the wind increase airspeed and/or climb rate?
At 5:24 to 6:10 in the video linked below, Kelsey appears to be claiming that turning into the wind tends to create 1) an increase in airspeed and 2) and an increase in climb rate.  Are either of these claims accurate?
Since Kelsey didn't say anything about the wind gradient, consider the case where the wind gradient is negligible, i.e. the case where the wind speed and direction are nearly constant over the altitude range of interest.
The case where the wind gradient is not negligible may be of some interest as well.  Though if the aircraft's vertical speed is very low, this would tend to suggest that even a significant wind gradient would have minimal effect on the aircraft's actual performance.

PS-- consider-- if you were actually at risk of sinking lower-- and there was a significant wind gradient-- which direction of flight, with respect to the wind, would minimize the sink rate?

A headwind doesn’t affect rate of climb (feet per minute) because your airspeed doesn’t change, but it will increase the angle of climb (feet per mile) due to the reduced ground speed.

Why are you dragging out this dead horse again?  Other than the video link to this specific snippet of commentary, the subject has been covered here in many other questions.  Nothing new here, and I'd vote to close as a dupe, but the system will force me to search for a specific dupe...

https://aviation.stackexchange.com/a/54983/60584


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Nose gear failure in single prop aircraft: belly landing or nose landing?
Let's say we are flying a single prop airplane with tricycle format retractable gear, such as a Mooney Bravo or a Piper Comache. The nose gear fails mid-flight and is unable to be lowered. Is it safer to attempt a belly landing, or to actually try and make use of the functional main landing gear? What is the standard procedure?

Edits and updates:

Here is the video of a very smooth looking nose landing with a RCMP Pilatus PC-12 I could find
Here is the video of a smooth looking belly landing find I could find

My major concern with the nose landing would be the increased risk of the nose digging in, causing a flip and/or the fuselage to break in half. As pointed out by @acpilot, the probability of this increases according to runway type.

There is no procedure that this situation has, so this may be entirely opinion based. Personally I'd leave the mains down and land on the nose. Gives better directional control at lower speeds and you don't have to replace as much skin/antennas when the repair bill comes around (but you will need a new prop/motor anyway). Especially for low-wing aircraft though because things like flaps hang below the aircraft and you can really tear up a lot in a belly landing.

Keep the fuel away from sparks. Then avoid sudden deceleration. So, if landing on other than hard surfaces, you may need to consider the chances of burying the nose and flipping. Personally, I'd leave my mains down and fly the nose on to a paved surface.  Repair bills aren't part of my thought process.  That's what insurance is for.

One the gear or engine fails, the insurer owns the airplane, and your only job as pilot is to limit injuries to yourself (and any passengers) as best you can.

The standard procedure is whatever is in the POH for your aircraft. This is from a C182RG POH:

LANDING WITH A DEFECTIVE NOSE GEAR (Or Flat Nose Tire)

Movable Load -- TRANSFER to baggage area.
Passenger -- MOVE to rear seat.
Before Landing Checklist -- COMPLETE.
Runway -- HARD SURFACE or SMOOTH SOD
Wing Flaps -- 40°
Cabin Doors -- UNLATCH PRIOR TO TOUCHDOWN.
Avionics Power and Master Switches -- OFF when landing is assured.
Land -- SLIGHTLY TAIL LOW.
Mixture -- IDLE CUT-OFF.
Ignition Switch -- OFF.
Fuel Selector Valve -- OFF.
Elevator Control -- HOLD NOSE OFF GROUND as long as possible.
Airplane -- EVACUATE as soon as it stops.

That assumes that you've already run the gear extension failure checklist without success, of course.

I really like the "Hold nose off ground as long as possible" recommendation. I usually hear "lower the nose gently", which is obvious, but having a non-arbitrary rule on when to actually put it down should definitely help.

While technically not one of the choices you asked about, you may not be aware of a quasi-third option you should consider.
Make a pass down the runway and "bang it on the mains" a couple of times to see if you can jolt the nose gear to go down and locked. If it works, go around WITHOUT RAISING THE GEAR and land normally (well, more like gingerly). Even if it doesn't work, you are no worse off than you started and this has the added benefit of burning off a pattern's worth of fuel (you'll want to burn fuel down to minimum reserves before committing to a landing to minimize stall speed and fire danger regardless) and gives you a look at the texture of the surface to help you with your original choice.
Additionally, if you do wind up landing without (nose|any) gear down, if the engine stops when you switch it off (not a given), try to position the propeller with a couple of bumps with the starter before touching it down such that is positioned to minimize contact with the ground to reduce the likelihood of digging in and flipping, as well as reduce the repair/inspection bill on the engine itself.

Typically in that situation, you would land with the gear down and lower the nose as gently to the ground as possible after touchdown.  Nose gear failures are the easiest of all gear up
landings to deal with.


text:
RC airplane required engine power
I'm going through the process of designing an RC airplane. I know that probably most calculations on scale models might be non-precise ones, but I'm trying to do it as correct as possible (it's a school project). I was trying to check how much shaft power I would need for the aircraft, so I did an excel table and used some pessimist assumptions in order to check if my 46 cubic inches, which deliveries 1,63HP, had enough power.
These are the aircraft parameters:
Chord= 0,3m
Wingspan = 1,8m
Wing Area= 0,54m2
AR=6
W= 3,7kg (assumed)
Cp = 0,048 (assumed)
Propeller efficiency= 0,6 (assumed)
Air density= 1,225 kg/m3 (Sea Level - where I intend to operate)
I used W = 1/2  *  rho  *  S  *  V2  * CL to identify the required CL for level flight at any given airspeed, then   Cdi = CL2 / (pi * AR *  e)  and using Ri =  1/2  * rho  *  S  *  V2  *  Cdi and
Ri =  1/2  * rho  *  S  *  V2  *  Cdi to find out both resistances I summed them up and multiply them by speed to get power, then I divided that power by propeller efficiency to get the needed shaft power.
For my surprise, the maximum speed that I could achieve with that 1,63HP it's between 39 and 40 m/s or 144km/h (89,4775 MPH), it seems like a lot.
Because of these results, I decided to contact a friend who is into RC Planes, he told me that that engine was actually too little for a 1,8m wingspan plane, it looks like I'm doing something wrong, but I don't know what. L/Ds actually make sense.
This is the link for the excel file

Do you mean 0.46 cubic inches? 50W/lb is normally considered the minimum for RC planes but you have 3 times that, which should be plenty of power for aerobatics.  For reference, here's a similar size model with a 10cc (0.60cubic inch) motor - https://alshobbies.co.uk/rc-planes/planes-fuel/fuel-sports-planes/Valiant-10cc-ARF-A-HAN5080

Yeah that's a 0.46 cubic inch engine, I spoke to someone with some experience, who recommended a 0.60 cubic inch for 1.8m wingspan, he told me that I can fly with a smaller engine, but I will have problems on windy days or taking off from a grass runway. He also told me that my model will probably end up weighting more than these 4kg

I think I'd agree with that. If you can build it light a 0.46 would be OK but most models that size use a 0.60 (10cc) 2-stroke or 0.90 4-stroke. You could try asking over at drones.stackexchange.com

I did not realized I got a specific page for that haha. Anyway, thank you for your help Robin.

Resistance is a term used in politics and electric circuits. We here talk of drag.
Your induced drag equation uses speed where the lift coefficient belongs:
$$c_{Di} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
What is missing now is the zero-lift drag which is the dominant contributor to overall drag at high speed. From your top speed result this seems to be
$$c_{D0}=\frac{2\cdot P\cdot\eta_{Prop}}{v_{max}^3\cdot S_{ref}\cdot\rho} = 0.040$$
assuming a propeller efficiency of 70% and neglecting induced drag. That figure is not unreasonable. Is the landing gear retractable?
Now we can write for the total drag as a function of speed:
$$D = \frac{\rho}{2}\cdot v^2\cdot S_{ref}\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
$$D = \frac{\rho}{2}\cdot v^2\cdot S_{ref}\cdot c_{D0} + \frac{2\cdot (m\cdot g)^2}{\rho\cdot v^2\cdot S_{ref}\cdot\pi\cdot AR\cdot\epsilon}$$
When sizing an engine the most reasonable parameter is power loading: How many Kilowatts are available per square meter of wing area and per Kilogram of airplane mass. Wingspan is a poor basis for comparison, since a larger span at the same area means a higher aspect ratio and lower demands for power. When using your figures, your power loading is 1.21 kW for 0.54 m² or 2.25 kW per m² or 0.608 kW per kg. Compare these figures to similar model aircraft to see whether you are on the right track.
Nomenclature:
$P\;\;\;\;\;\;\:$engine power
$v\;\;\;\;\;\;\;$flight speed
$\rho\;\;\;\;\;\;\;$air density
$c_{Di}\;\;\;\;\;$induced drag coefficient
$c_{D0}\;\;\;\;\:$zero lift drag coefficient
$S_{ref}\;\;\;$reference area
$AR\;\;\;\;$aspect ratio (= 6 in your case)
$\epsilon\;\;\;\;\;\;\;$span efficiency, use 0.85 for a rectangular wing
$m\;\;\;\;\;\;$airplane mass
$g\;\;\;\;\;\;\:$gravitational acceleration

Hey thank you for your answers you are being really helpful, I really appreciate that.

About resistance instead of drag that's my Spanish playing its part, we use the same word for both resistance and drag, and that word is similar to resistance hahaha.

I did use Cl in Cdi equation, I made a mistake when typing it. Is that zero lift drag the same that parasite drag or should I sum both of them up?

I did realise induced drag did almost nothing compared to parasite drag at high speeds

@LucasDelgado. The zero lift drag coefficient is all the drag the airplane produces without creating any lift, referenced to dynamic pressure and reference area. So it sums up everything except induced drag, parasitic drag included.

Ok, I always called the whole thing parasite drag. Oh and the aircraft is not supposed to have a retractable landing gear.

@Then your drag numbers are awfully optimistic.

Ok that explains the optimistic results, I will try to investigate more and get to a more realistic number. Thank you so much for all your help


text:
F-15 APU or JFS
Can a portable GTCP-85 series be used on an F-15? Or is there no capability to use an external APU. As I understand, F-15's use the JFS-190?

You have two questions here that should be separated in two posts.

Thank you for responding to my format style, it's been adjusted. Now can you provide any insight to the question? This should be interesting.

Any jet fighter aircraft can use an external APU that provides the appropriate voltage and amperage. Generally an APU is defined as a device that provides electrical power, and in some cases (such as the APU on a CH-46 helicopter) also hydraulic power. The JFS-190 is different in that it is intended to help start the engines. It provides hydraulic power and mechanical power to start the engines using clutch plates.

I believe I have found the answer. F-15's use Generator Set, Gas Turbine Engine Model A/M32A-60A nsn 6115-00-420-8486. FInally someone on flight line was able to assist. But thanks for your help amigo!

Cool beans, glad you found what you wanted.


text:
What is the FAA regulation for the 3 mile / 1,000' separation for a commercial airliner?
I need help finding the Number/Citation for the FAA regulation/order that states commercial airliner separation should usually be at least 3 miles laterally, or 1,000 feet vertically.
I cannot find anything that clearly states the **"or" part.**

The title states the minimum safe distance, so the question clearly isn't, "How much is the minimum safe distance between two planes in flight?"

The accepted answer on that question is very thorough, and gives exactly the references asked for in this question. When closed, this question is still searchable/findable, even though the answer will be one more click away. VTC as a dupe.

@ymb1 sounds good.  I just worry sometimes that I'm seeing valuable specifics indefinitely swept under the rug due to similar topics having been asked in the past.  I know this isn't the place for the discussion, so maybe I'll put a question on meta sometime. Thanks.


text:
Asymptomatic Cavernous Malformation been approved for Class 1, 2 or 3 Medical?
Anyone here with a asymptomatic cavernous malformation been approved for PPL, CPL or ATP?
Recently was concerned with the symmetry of my eyes changing. Opthamologiest ordered an MRI that incidentally showed a small left medial parietal cavernous malformation. This just as I was applying for my PPL medical! The vanity of it all! lol. Anyways, no symptoms, benign, no medications, no treatment suggested.
I'm hoping it won't be procedural denial and turn into a costly and lengthy appeal. Anyone have info to share please?

Medical certificates are separate from pilot certificates (licenses).

It's unlikely someone here will know how this affects your chances. You should just talk to an AME about it. Good luck!

Already met with the AME. I'm looking to hear other people's stories.

My instructor is completely blind on one eye, had to get a special issuance for his class II but he flys commercially as a CFI and is going onto the airlines soon so I’d say it can be done.

Do you have an update on how this turned out for you?

Hi Nick,  I decided not to pursue it after speaking with a consultant who specializes in issuances from the FAA (He was a previous FAA employee). The FAA would likely require 2 year of monitoring with many costly procedures and other fees that will come along with it. Being I'm 44, I don't feel the time line is acceptable to trajectory I had for myself. And of course, the time and cost of pursuing my ATP during that 2 years along with the possibility of being declined or my licensed pulled during my career is not a risk I'm willing to take.


text:
Efficiency of Flyboard engine
From what I understand (not much), you need good specific impulse to travel long distances with, say, flyboard.
I know that RP1 has good specific impulse. I wonder if he used it, and what type of oxidizer/propellant would be most efficient for this task, and feasible (very small engine, not that high temp) .
To be specific: The question is if the efficiency (in terms of travel distance per unit mass of fuel) could be improved by choosing another type of engine/fuel?

Can you be more specific on what your question is?  I'm not sure I understand what you are asking.  Also, you may be confused between jets and rockets.  Flyboard is powered by a jet, which uses ordinary air from the atmosphere as the oxidizer.  Rockets in space have to carry separate oxidizers, but jets do not.

Yes, it is reasonable . My main interest is rockets, so I didn't even think about it.

Using a rocket engine with another oxidizer is out of question?

I'm not directly familiar with the engines Zapata uses on the Flyboard Air, but I'd hope they're using a kerosene derivative like JP-1 or commercial Jet-A.  Alternatives (gasoline, diesel, various alcohols) have no better energy content per volume, and some (alcohols) considerably less.
There is no case (for low altitude atmospheric flight) in which a rocket can beat an air-breathing jet for specific impulse/specific fuel consumption -- because of the need to carry oxidizer, instead of just using the air for that purpose, the amount of fuel/oxidizer available is limited by tankage.  This is why airliners, warplanes, and private business aircraft use jets or turbine driven propeller engines instead of rockets (not to mention the far higher durability of a turbine compared to a rocket engine).

Your answer is very good. I guess that we can dive into various options involving battery and I guess that compared to these cases too, jet is considerably better.

Fossil fuels beat the energy density of the best batteries by a factor of, as I recall, five or six.  The small efficiency increase of a fan or ducted fan vs. a jet is nothing by comparison.

@ZeissIkon By a factor of 20. This is how you get 20,000 km jets, but only 1,000 km is potentially achievable for an electric aircraft.

According to an old copy of their web site, it runs on Jet B.

For rockets, specific impulse is constant regardless of speed.  For jet engines, specific impulse is very high at zero speed and drops off as velocity increases. At relatively low speeds (say below Mach 1), a jet engine will beat the pants off a rocket in terms of specific impulse (i.e. better by a factor of 20 or more). See for example some comparisons here: https://en.wikibooks.org/wiki/Jet_Propulsion/Performance  Since the flyboard is definitely a low speed craft, you would not improve it by using a rocket instead of a jet.

Feasible, but then you have to carry rocket fuel and oxidizer (such as liquid Hydrogen and liquid Oxygen, both refridgerated and under pressure), vs just readily available fuel (Jet-A), and getting oxidizer (O2) from the air all around us.

You seem to be conflating a turbojet with a rocket.  Because the jet uses atmospheric air as its oxidizer, its apparent specific impulse is many times even hydrolox rockets.


text:
What are those bumps on top of the Antonov-225?
What are those bumps on top of the Antonov-225? What are they for? And what are they called?

"The smaller semi-spherical domes further aft were caused by passengers not wearing seatbelts during turbulent conditions." -- retardo montalban.

According to the Airliners.net forum, they are fairings that cover hardpoints used for attaching outsize loads.

Outsize loads that cannot fit into the capacious cabin (including Buran and Energiya components) are carried 'piggyback', the load supported on two main attachments above the center section. These supports and other smaller ones along the fuselage top are faired over when not in use.

The text is quoted from aeronautics.ru (web archive link).
Please note that the two large ones were not used for carrying the Buran space shuttle, as shown in the photo posted below. (More pictures here.)

Is there any evidence of them ever being used outside of the Buran program? Or a photo of them being used with the Buran?

I don't know about actual use. There's a schematic here that shows other loads mounted on top.

Very interesting, thank you! I really want to know what the red teardrop shaped tank is, with some weird mini-buran?!

Had I scrolled further I would have realized that it is the MAKS https://en.wikipedia.org/wiki/MAKS_(spacecraft)


text:
Wing loading in conceptual design

Is it possible to have a minimum wing loading at climb segment of our design aircraft (air superiority)?
Which segment would have minimum wing loading i.e. climb, take off, cruise, instantaneous turn, sustained turn, etc?

To have a minimum wing loading in climb you're going to be burning a lot more fuel.  I suspect Vy maximum rate of climb would still be using the wing.  Study of maximum altitude record setting techniques may shed some light on this.  A race between a (lower drag) jet and an F16 would be interesting, but the smaller winged (F-104) may need more fuel (weight) to reach the same altitude.  I would bet on the F16.

From lowest to highest wing loading:

Climb: if a fixed wing plane and the nose is pointing up, some of the vertical force must be generated by the thrust.
Cruise: the lift must only compensate for the weight.
Inducing a turn: the rolling velocity has very little effect on wing loading.
Take-off: a slight positive g-loading during the nose-up motion.
Sustained turn: up to the maximum design load factor. 2.5g for passenger aeroplanes, up to 9g for fighter jets, with a proportionately greater wing loading that that in cruise.

Why "up to 2g"? As much as the aircraft holds! If this is "air superiority", it should take 9g or so. By the same token, it should be able to climb vertically, or just about, with zero wing loading.

@Zeus Indeed, corrected.

Small nitpick, harkening back to questions regarding lift in a climb, it is more efficient to use the wing to climb up to a point where vertical lift becomes so small (very steep climb angle), then it is more efficient to reduce AOA and climb with thrust only.  But if using wing to climb (as well as thrust vertical vector), loading may be greater than (lower AOA) cruise.


text:
Exceeded myopia limit on UK CAA Class 1 Medical, am I still eligible?
I am 17 and this may sound stupid but my vision in my left eye is -4.50, and my right eye is -7. My right eye exceeds the limit of -6 by just 1, I am following off the UK CAA guidelines as I hope to become an airline pilot in the UK. Does the fact that my eye misses the limit by -1 completely erase my chances of becoming a pilot? I have contacted various aeromedical centres regarding this too. But I would also like to hear from other  pilots who are in a similar situation.

Are you correctable to 20/20 with glasses?

Consider this: If your navigation is off by just 1 degree, over a long enough distance, you'll end up at the wrong airport (or at no airport at all). Just because you're "really close", doesn't mean it's acceptable. Though, as @JohnK asked, I believe the question is what is your corrected vision, not uncorrected vision.

Nobody actually flies that way in the real world.  The standard for a pilot holding a heading is +/-5 deg, and wet compasses can be off by up to 10 and be legal.

Yes my vision can easily be corrected to 20/20 with contact lenses or glasses.

You are evaluated on corrected vision, not raw.


text:
Does a Boeing 737-800 Have a Ram Air Turbine (RAT)?
I am travelling with Thomson on a Boeing 737-800 and wondered if it had a RAT?

No it does not, it does not need one, there is a mechanical connection to the flight controls that can be used if all else fails.

The B737 flight controls are hydraulically powered.
There are three hydraulic systems: System A, System B, and Standby. Only one main system (A or B) is required for hydraulically flying the aircraft, during normal operation they are both operational.
The two main hydraulic systems have an Engine Driven Pump (EDP), which can continue delivering hydraulic pressure when the associated engine is windmilling. All three hydraulic systems are also powered by their own Electric Motor Driven Pump (EMDP).
In case of dual engine failure the APU can power the electrical systems for the EMDPs, still delivering full hydraulic power.
If the fuel has run out and the APU cannot operate, two batteries provide at least 60 minutes of backup power for the electrical systems. The EDMPs can be powered in this stage, however they provide a high load.
If all fuel is gone and the batteries are depleted, the aircraft can be flown by hand, directly overcoming the aeroforces by pulling hard! This is called manual reversion.
In manual reversion, the aileron trim tabs now function as geared tabs, assisting in overcoming the aeroforces. Elevators will have high aeroforces, high friction forces, and freeplay around centre point. Stabiliser trim wheels provide additional pitch control. The rudder has no manual reversion.

The A320 flight control system are powered in a pretty similar way except for the manual reversion - as a last resort the RAT is deployed for powering the backup hydraulic system. The A320 has no direct mechanical link to the elevators and ailerons, only to the rudder.
Image source

I'm pretty sure the battery only says BATTERY.

Small point: with no generators & no APU, the battery/batteries do NOT power the standby hydraulic pump. That'd be way too much load. If it's only loss of all generators, you have the EDP's to power hydraulics; if both engines have failed with the APU deferred (boy are you having a bad day) you'd still have some hydraulic pressure from the fans windmilling. And, bright side, no asymmetric thrust to counter with the rudder in that scenario!

@RalphJ Thx, have included into answer.

Interesting... there have been a few airliner crashes resulting from loss of all hydraulic fluid, and consequent loss of control. They could have used a manual reversion system. A bit of control is better than no control. Quite a few A10's made it home on manual reversion when their hydraulics were shot out.

@tj1000 Yes UA232. B737 would be about the largest aircraft where manual reversion is an option.

@Koyovis, lot of non comparable things. « The A320 flight control system is pretty similar except for the manual reversion »: no A320 has FBW flight controls so totally different even though requiring the hydraulics. « the A320 has no direct mechanical link to the elevators and ailerons, only to the rudder »: true but incomplete, in last resort (total electrical power loss) it has too a mechanical command to the stab trim, it operates directly the hydraulic valves and is very soft to use, to the contrary of the 737-800 which has very small trim wheels, very hard to drive the trim screw

@user40476 Yes indeed, fly by wire. The hydraulic bit is very similar though, with its Green and Blue and Yellow hydraulic systems. Rudder and trim wheels to stab trim are almost identical.

@Koyovis.   , no , the trim wheels operations are totally different: the 737 wheel should drive directly the trim screw which requires tremendous effort with the small wheel on the 800 compared to the 1st generation of the 737( same problem with the max). On the 320 the wheels have no handle because the wheel is not driving the screw, but a hydraulic valve block that’s why it is very soft.

@user40476: ...which means that losing all hydraulics means you also lose stabber trim.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why didn't LO7898 fly near the North Pole?
I've seen LO7898's route from Seoul to Warsaw on flightradar24. Instead of flying the shortest route (over Mongolia, Russia and near the North Pole) it flew as if Earth was a cylinder: over China, Kazakhstan and so on, simply westwards as if Earth was cylindric. It looked to me as if they wanted to avoid flying over Russia, but why would they want that? Did Mongolia and/or Russia forbid LOT (Polish Airlines) to fly over their soil, and why?

Why the many downvotes? Perhaps it would still be a shorter route if the plane went around Russia north of it, close to the North Pole, not south.

Since you seem not to be aware, the Russian airspace is closed to LOT  and others because of the war in Ukraine.
Because of the war, EU countries (and a few more) closed their airspace to Russian airlines.
As a tit for tat, Russia closed its airspace to airlines of those countries.
This includes Poland, and thus, LOT.
https://www.euronews.com/travel/2022/02/27/russia-closes-airspace-to-planes-from-several-eu-countries
https://www.airport-technology.com/news/russia-shuts-airspace/
https://www.bbc.co.uk/news/world-europe-60539303


text:
Why is the runway at Ulyanovsk Vostochny Airport so long and wide?
According to Wikipedia, the runway at the Ulyanovsk Vostochny Airport is tied for longest in the world (at 5000 meters/16,000 feet), in addition to being the widest (at 105 meters/344 feet).
It's not clear to me why this is the case: usually a very long runway is required at high altitudes or in hot climates, and neither is the case for Ulyanovsk. The Shuttle Landing Facility is also particularly long and wide but it was built for a special application (and it doesn't even make it in the top 10 in that list). Was the runway at Ulyanovsk also built for a special purpose? It can't be for the sake of the An-124s manufactured nearby, as those (obviously) can operate from conventional runways.

The runway is designed for flight testing.  Zhukovsky airport and Edwards Air Force Base also have a very long, low altitude runway for the same reason.
If you are testing a large or fast aircraft, you want to have a lot of space to land in case the controls are not as good as intended.

It can also be hot at Edwards.


text:
Why could a Rotax 914 light aircraft lose power at 7000 feet?
I was flying an RV 4 equipped with Rotax 914 engine and variable pitch propeller.
The problem was observed during flight above 7000 feet; vertical speed became 0, RPM overshoot for 2, 3 seconds to 6300 when the turbo engaged for gaining height. I did make an effort for turbo but was not gaining height. It felt like under power, but take off was normal. Air Box target pressure was normal. All other engine parameters  also normal. So I came back to pavilion.
Could you please suggest possible causes?

Turbo wastegate probably stuck open.

You seem to have exceeded the engine max. rpm by 9%, so best have your engine checked anyway...
As for the lack of boost, there might be a loose connector or a crack in the pipework after the turbo.


text:
Taper sweep angle
Is the Taper sweep angle the same as the sweep angle?
So I know that the sweep angle is the angle from the vertical line from the leading edge to leading edge wing line.

"So I know that the sweep angle is the angle from the vertical line from the leading edge to leading edge wing line."-- I can't quite understand what this is saying, but it appears to be incorrect.

Re "Taper sweep angle" --I know what taper is, and what sweep (or sweep angle) is, but have never heard of "taper sweep angle"--

Hi, yeah I’ve never heard of Taper sweep angle but I came across it when a teacher said it

Could it be that the teacher meant "sweep angle" and said something like  "... taper, erm, I mean, sweep angle ...". Or was the language spoken not English, so there might be potential for misunderstanding terms or translating them?

Hi, he said it in one sentence, without pause and then wrote it down too- I sent him an email but he doesn’t reply usually

May I ask what level of school is this? Highschool maybe?

Yeah high school, physics teacher said it

Then it is totally possible the teacher has no idea of what he/she is talkin about...

"Taper angle," "taper sweep angle," etc., have no widely accepted definition.
Sweep angle could be defined as the angle of the leading edge or of the trailing edge, but it's traditionally that of the 25% chord line, because that's close to the aerodynamic center.  In other words, that definition reduces how any taper present might affect what the sweep results in.
When taper is defined as just a tip-to-root ratio, not anything about angles, then the effects of sweep and taper can be discussed more independently.

Image source, earlier used in this answer
The sweep angle $\Lambda $is the angle that the quarter chord line makes with the lateral axis of the aeroplane. As can be seen in the pic, the leading edge and trailing edge of the wing have different angles relative to the lateral axis, due to the taper.
Wing taper $\lambda$ is the ratio between chord at the wing root and chord at the wing tip - this ratio does not define an angle yet, only when multiplied by the wing span.

The leading edge angle $\Lambda_{LE}$ of a tapered wing with zero sweep angle is defined by: $$ tan (\Lambda_{LE}) = \frac{¼(c_r - c_t)}{½ b}$$ And of the trailing edge $$ tan (\Lambda_{TE}) = \frac{¾(c_r - c_t)}{½ b} $$ So the "taper sweep angle" could be defined as $\Lambda + \Lambda_{LE}$ for the leading edge, and $\Lambda - \Lambda_{TE}$ for the trailing edge. I've never have heard Taper Sweep Angle referenced before, but it could be coined this way.

Taper angle is more of a machining term, which might be the easiest described as the tip angle of a cone formed by a tapered section of a pipe (or tube). Well, maybe not that clear but anyway. For a wing we could logically use the same kind of definition:
Taper angle would be the angle two imaginary lines, drawn along leading edge and trailing edge and extended beyond the wing tip, make when they intersect.
But as stated in comments, this is not a common aviation term, if one at all...

So, the angle between LE and TE?  That would be more precise than taper ratio, which depends on wingspan.

Oops, I was sloppy writing that, I'll fix it. Thanks @CamilleGoudeseune


text:
CoG Envelope Calculation - Am I Doing Something Wrong?
I'm doing some pre-planning for a bush flight with the Icon A5, and I'm at CoG calculation.
This is the W&B form from the A5's POH:
I weigh 225 lbs.  I'm simulating 111.6 lbs of gear which can be distributed between the luggage shelf and the passenger's seat. I then will bring the aircraft to MTOW with fuel.
My W&B looks like this:
Moment Calculation

Position
Weight
Arm
Moment

Dry Weight
1080
154.75
167130

Pilot
225
128.5
28912.5

Passenger
0
128.5
0

Usable Fuel
91.7
153
14030.1

Baggage
111.6
157
17521.2

Garmin
1.7
109.7
186.49

Totals
1509.6

227780.29

TOW 1,510
CG Pos  150.85"
Which puts the CG nearly 3 full inches outside the envelope:

I've messed with the numbers a several ways, but no matter how I do, I can't get the CoG back in the envelope.
Am I missing something about the calculation process here, or is there basically no safe configuration of the A5 with a 225lb pilot?
I will note that MS Flight Simulator 2020 doesn't consider the CoG out of limits (it gets mad at you if it does) but I can definitely tell that takeoff performance is greatly impacted and god help me if I try to takeoff with any kind of right crosswind.

The pilot station is a good ways forward of the CG range, are you sure that’s right?  Because even though you’re a pretty big dude, two adults will generally exceed 225.  Does the POH mention a weight limit for people? I’m trusting your math, but the crew arm seems suspect to me. (although in photos you do sit fwd of the quarter chord.)  What’s a twitch channel?

Where did you get the dry weight arm?

P.S.  If you don't get a good answer here call Icon - present the same question and tell them you are thinking about buying one, but only if you can fly with CG in limits!

I'm putting this in a comment as I don't have time to write anything definitive. I think your dry weight arm is incorrect. You've used the reference datum from the POH, where the actual CG is measured using a process defined in the POH section "EMPTY WEIGHT AND CG MEASUREMENT WHILE ON GEAR".

@GdD As you correctly inferred, I have no physical plane to put on a scale to get the exact measurement, so I just assume the platonic, factory-spec A5 will have it's dry weight at that point.  They don't provide a point that I can find as the spec-point. If you can suggest anything else to use as a stand-in that'd be helpful. Otherwise the answer may be "This level of realism can't be simulated."

@MichaelHall The POH makes no such mention, no. But yeah, it feels like I must be doing SOMETHING wrong, for that reason. But I read the thing four times and couldn't figure out what.

@MichaelHall Twitch is a streaming platform, mostly for folks streaming videogame content. (e.g. I'm at twitch.tv/phdipo on Thursdays from 7-10 ET)

the CG is too far forward, which is surprising. Something is wrong with your empty weight numbers. What's the source?

Yes, you are doing something wrong.
Your biggest mistake is using 154.75 as the empty weight moment. As shown in my last image (from the Icon A5 user manual), 154.75 is just a reference datum marking where the forward face of the spar is located. It has nothing to do with the empty weight moment.
Your second mistake is putting too much weight in the baggage area.
I have included here an actual weight and balance done by the NTSB of an Icon A5 that was involved in an accident. The empty arm was 163.8 and is probably typical of all Icon A5 aircraft.
As you can see from the calculations, the Icon A5 has a poor useful load and it is difficult to carry 2 pilots, with a reasonable amount of fuel and baggage and remain under the 1510 lbs max gross weight.
NTSB report for N663BA, ICON A5

That REALLY is a limited useful load.  If the pilot weighs much over 200 lbs, you can have a child in the other seat at most, or else you're flying solo.  Wow!

First, the reference datum for the spar is of no consequence in W&B calculations.
For Empty Weight and Moment, you have to refer to the actual W&B record for the specific aircraft. It is part of the POH or the Approved Flight Manual (the one with the a/c serial number on it.) I suspect (reinforced by the exercise below) that not having the proper values for the empty weight is the root of your problem.
The other issue is that as you stated; "111.6 lbs. of gear which can be distributed between the luggage shelf and the passenger's seat." Yet, in your W&B calculation, you put it all under baggage. For this exercise, I'll assume your original empty weight numbers to be correct.
The problem is that the POH limits the cargo shelf/baggage area to 60 lbs., with the following:

WARNING: Loading a concentrated weight fully aft in the baggage area
may cause an unsafe aft CG condition.

If you put 60 lbs. in the baggage area (@ 157 in.) and 51.6 lbs. in the passenger seat (@ 128.5 in.) it will move the CG forward. Without changing any of your other numbers, that will result in a CG at 149.9 in. which is even further out than your first effort.

@MikeSowsun You are correct. I have updated my answer.

Yeah, I forgot to mention that I'd stress-tested the assumptions by overloading the baggage, for the reasons that you arrived at. I'm still waiting for ICON to get back to me, because the problem with simulation is you don't have an aircraft to weigh.


text:
When and for what purpose APU is used on the ground?
When watching the below clip:

at exactly 11:02, FO says that APU is not required.
What could be the reason for using APU on the ground? What good could this bring? EDIT: Both questions concerning depicted situation only -- i.e. a plane has landed in a quite very hot air.
I am a total noob to flying, but I was always more than sure that APU is used in air only. It is used to produce minimum electrical power to on-board equipment. Which means (as I assume) that there is zero electrical power when starting APU and it must be started when flying airplane generates enough airflow (through APU).
What am I missing? In which scenarios (EDIT: for depicted, landed airplane conditions) on the ground APU "could be required"? And how a ground speed of the after-landing rolling plane (very limited to airborne speed), generating minimum airflow, could start up the APU?

Starting the engines, air conditioning, AC power if no ground power unit

@trejder Your understanding of APU starting is incorrect. An APU is started using electrical power from either a battery,  or the aircraft engine generator. You can not start an APU using airflow.

@tedioustortoise The plane in question is rolling through airport after 9+ hours flight. Has both engines fully operational (no need to start them) and providing electrical power, has air conditioning working.

@MikeSowsun No, it does not. The only on-the-ground reference that I found is starting the engines and providing the AC power (not need after landing) or landing in a very cold conditions (here we have 86F).

@trejder I was more answering the generic question - in which scenarios is APU on the ground required.

@MikeSowsun Your comment sounds like a great answer! :)

Thanks. Done…. :)

It is very common for an arriving airliner to start the APU just before arriving at the gate. This allows the engines to be shut down immediately when the aircraft reaches the gate.
Waiting for ground power to be hooked up can sometimes take a few minutes. Leaving the engines running at the gate is very noisy, burns considerable fuel, creates an unnecessary safety hazard, and delays the offloading of baggage.
Even once ground power is connected, many operators will leave the APU running for heating or air conditioning. (adequate heat or AC may not be readily available)

In RJ land, it's common when flying with the APU deferred to leave the right engine running if a ground A/C cart or huffer cart isn't available at the gate. Is that ever done with heavies?

Most airports in Europe prohibit the use of the APU when the aircraft is parked at their gate for noise and environmental reasons. They can only use it in case of a problem with the aircraft or ground equipment. You would never operate deboarding operations with an engine running, the doors are inside the hazard zone.

The APU is primarily used on the ground for:

Engine Starting - the main engines need a bleed air source of pressurised air to get them “turning” before fuel is added and they become self sustaining. Ground starter units can be used, but it is not economical or practical.
Air conditioning - airports may provide air conditioning sources which attach onto the aircraft. But again, most practically the APU provides the pressurised bleed air for air conditioning to the cabin.
AC power. Typically ground power units are provided at airports, but in their absence, or in the interim period between disconnecting all ground support units and engine start, the APU will provide AC electrical power to the aircraft. (The battery with inverters to AC power typically only powers limited resources on larger aircraft).

Thank you for a very quick and complex answer. I have updated my question to narrow it down to depicted situation only (landed airplane rolling through airport). Can you update your answer to reflect that? If not (meaning that there are no scenarios for landed airplane to use APU) then simply reflect that this is just a procedural wording and APU is never used on the ground for a just landed airplane. Thank you.

@trejder thanks. I will have a look tomorrow (it’s late here), but no doubt someone else might have got an answer in too in the meantime. :)

Waiting for you (or someone else). Will be happy to reward you with +25. Good night (and remember to keep it above the horizon! :)

TLDR: It replaces "ground support" at less well equipped airports, or unequipped aprons.
The APU starts the main engines
Start with this: Your car has a battery, it starts the engine.  Batteries on airplanes aren't big enough to start the main engines.
So the APU is a small engine that the batteries can start.  The APU can then start the main engines.
But it also provides hotel power...
Once the APU is running, it also provides hydraulics, electrical controls, lighting and compressed air for engine start and air conditioning/heat for the cabin.  It can also be used to power these hotel loads during takeoff, to avoid bleeding energy from engines.  Or during flight, as famously used in the Flight 1549 ditching.
Before an airplane can be boarded, the HVAC must be run for quite some time to make the space habitable. You've heard warnings about not leaving babies or dogs in cars - same thing will happen to an airplane cabin left in the sun. That cabin could rise to 60-70C (140-160F) and you cannot board people into that!
Heating is simply: compressed air is pretty warm.  Air conditioning uses a machine called a PACK.
If an airplane expects to sit on the ground for an extended period, they will usually shut off the main engines and run the APU to save fuel and engine hours.
...except at better-equipped airports
Shore-side equipment can deliver electrical and/or high-volume compressed air to a jetliner.  The latter both starts engines and powers the heat and air conditioning.
The compressed air comes from a machine informally called a "huffer" - if you saw Top Gun: Maverick, you saw them start up a "huffer" to start up a jet fighter.
Simpler versions of this shore electric and air supply is a portable cart that is basically an APU on wheels.  Better versions are built right into the apron or gate and are coming off grid power or a central air source. The huffer may be local to the gate, but electric.


text:
How safe is the Certified Rotax 912 versus the Continental O-200?
I'm thinking of buying a taildragger LSA, many of which have a Rotax engine. Continental and Lycoming are the major suppliers of certified piston aircraft engines, and they are considered to be safe engines (for pistons!). I'm wondering if I should consider the safety and reliability of the certified Rotax engine to be substantially worse than that of the Conti O-200 (the only other certified LSA engine), and if there is any evidence one way or the other.

I personally out of experience prefer Rotax engines over most other engines. They are a lot different to most but that makes them better not worse! Plus I have been talking about Rotax engines to a lot of people at the flight school I'm currently at, and they all prefer Rotax. If well maintained you can definitely trust them! Thats just an opinion though, can't give you a fact based answer :/

As far as I can find out, no one knows. There's no good data available on engine reliability from the manufacturers - although they usually don't share that information anyway - and nothing substantial that I could find from any third parties.
There is some information online, although it's mostly opinions and there's no real, consistent data to support it. This 2008 article compared LSA engine options including the Rotax and said that there were more incidents involving Rotaxes than Jabiru engines (excluding non-engine related causes), but there were also many more Rotaxes in service so the comparison isn't meaningful.
In fact, the article said that any comparison is difficult because the Rotax was (is?) primarily used in experimental aircraft:

The great problem in identifying engine-specific problems is that in
  the majority of installations, the engines power
  experimental/amateur-built category aircraft, where differences in
  mounting, accessory placement, cooling and vibration variations can
  instill issues that vary from one installation to another

And it also made the point that there are plenty of engine-related incidents involving Continentals:

And accidents involving Continental O-200-powered craft were as
  numerous as you'd expect for the length and depth of its presence in
  general aviation aircraft. Here again, many occurred through no fault
  of the engine. Still, numerous reports involved engine stoppages,
  heat-related power loss and other engine problems.

The article's conclusion seems to be that a Rotax engine is not (was not) significantly different from any other engine:

To paraphrase the words of one long-time Rotax service-center
  operator, the main problems involving the engines stem from many of
  the same types of problems—poor judgment, misuse, mismanagement and
  poor maintenance—befalling all aircraft.

I found various other forum discussions about engine noise (no conclusion), fuel efficiency (Rotax is better), maintenance costs (some preference for Rotax) and so on, but nothing authoritative. I suspect that a detailed, data-based comparison simply doesn't exist; finding anything for Lycoming vs Continental is difficult, even with the much longer history and larger installed base.
In general, engine comparisons seem to be mostly based on opinion and anecdote (as described here). That doesn't mean the information is useless, but you do have to spend some time sifting and weighing the opinions to reach your own conclusions.

Ron Wanttaja wrote an article about the subject in December 2022, analyzing accidents in the Experimental/Amateur-built category in the United States, based on the FAA accident database. I know that you are looking for information about the certified motors, but to my knowledge there shouldn't be any mechanical difference between a certified and non-certified Rotax 912 or Continental O-200.
The article is behind a paywall (I think), but the gist is:

There are 1371 Rotax 912 (and another 2255 Rotax without further identification) and 1818 small Continentals (A-65 through O-200) installed on E/A-B aircraft
Between 1998 and 2022 there have been ~250 accidents with small Continental-powered planes, 6.4% of which due to engines issues, and ~370 with Rotax 912-powered planes, 5.1% due to engine issues. Engine issues here means mechanical failures, not e.g. power loss due to fuel starvation
The absolute numbers are very small (16 for Continental, 19 for Rotax) and show slightly more oil- and carburetor-related issues on the Rotax (mostly attributable to builder or maintainer error), more core engine and ignition issues for the Continentals

Wanttaja concludes that the Rotax 912 is safer/more reliable than the Continentals in general, and that there is no difference if you only look at the O-200:

As far as the small Continentals are concerned—well, the replacement is here. Data shows the Rotax 912 has better reliability than the traditional workhorses.
However, our “Continental” category suffered by lumping a number of different models together. Looking just at the O-200, the Rotax 912 and the O-200 have nearly identical statistics.

haven't read the report, yet 16 cases out of 1800 are 0.9%, while 19 out of 1370 are nearly 1.4%, so the conclusion is a bit odd? Then again, i don't know how many engine failures did not lead to an accident. Eg. if they all had 500 engine failures and happened to land well anyway, then my conclusion isn't so meaningful...

He also states "Of the cases where a Rotax-powered aircraft does have its engine model included, over half are Rotax 912s. So there are likely to be another thousand 912s in the homebuilt fleet." That puts the Rotaxes at 0.8%, but that's still very close to the 0.9% of the Continentals. I'd say pilot and owner decision making have a much bigger impact on the engine's reliability than the engine itself.

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